1. Field of the Invention
The present invention relates to an image sensing apparatus and an image sensing system equipped with the image sensing apparatus.
2. Description of the Related Art
An image sensing apparatus such as a CMOS image sensor requires a high-frequency clock for transfer in order to increase output speed of an image signal. However, when clock frequency is increased, it becomes impossible to ignore parasitic resistance and parasitic capacitance of a common readout line transmitting a signal from a pixel in the horizontal direction, thus the time required to charge and discharge the capacitance cannot be ignored. This is observed, for example, as a blunted waveform of an output signal from the image sensing apparatus or a signal within the image sensing apparatus.
The clock signal frequency, when it becomes higher than a certain level, causes a phenomenon in which a level of a signal waveform does not return to its original level until a next signal is input. Examples of inventions made to deal with this phenomenon can be seen in Japanese Patent Laid-Open No. 2003-234957. The invention has a differential amplifier circuit in an output stage of an image sensing apparatus to provide as accurate a signal as possible even if a signal waveform is blunted. However, to further increase output speed of an image signal, further innovation is required.